1. Field of the Invention
The invention relates generally to the assembling and replacing wear parts in apparatus for processing bulk type materials, and particularly to attaching flights in material processing apparatus, such as mixing and drying drums. A particular use for the subject matter of the invention resides in mixing and drying apparatus used for manufacturing asphaltic type paving materials.
2. Discussion of the Prior Art
Asphalt mixing and drying drums are typically cylindrical drums which are operated in a generally horizontal position. Material, such as crushed stone aggregate is typically fed into one end of the drum, is heated, then typically mixed with asphalt in a downstream end of the drum and discharged from the drum. A heater at one end of the drum typically generates hot gases which flow through the length of the drum. Mixing the aggregate within the drum is achieved by rotating the drum about its substantially horizontal, longitudinal axis, thereby advancing and agitating the aggregate material. In advancing through the drum, the material is lifted by flights which are spacedly attached around the inner wall of the drum, then gradually released from the flights, either to fall in a curtain of material through a stream of the hot gases, or released over the tops of the flights in a swirling motion to mix with asphalt or with other aggregate materials. The type of action is typically determined by the type of flights attached to the inside walls of such drums.
It is readily realized that flights attached to the inside of such drums are exposed to extreme wear which is the result of abrasive, sliding contact with the material, as the material first falls against the lower ones of the flights, then slides across upper surfaces of the fights, as the drum rotates and the flights move through an upper arc of a complete revolution of the drum. Wear is particularly evident on inwardly extending portions of the flights, while the portions of the flights directly adjacent the inside wall of the drum tend to experience less wear. Within relatively short time periods, the flights become worn and need to be replaced with new ones. So-called downtime for maintenance of the drums is, consequently, a function to be reckoned with in considering the value of the drums. The time required for maintenance to replace worn sets of flights amounts to a corresponding period of time during which the respective apparatus is taken out of service and is not available for useful production of materials.
It is, consequently, desirable to reduce down-time for maintenance and thereby extend the time during which such drums are available for production. According to one known technique of attaching flights to the inside of drums, the flights are attached with bolts and nuts to ears or brackets which are typically welded to the inside walls of the drums. The brackets extend from the walls towards the interior of the drums. When time comes to replace the flights, the heads of the bolts are typically burned off with a cutting torch and the worn flights are then replaced with new ones. Though typically accumulating material at the juncture of the brackets and the drum wall shields the portions of the brackets which are directly adjacent the drum, inwardly extending portions of the brackets are nevertheless exposed to the abrasive movement of material just as the flights are, and are, hence, subject to a similar, high degree of wear. It is very likely that in short order, after the flights have been replaced a few times, major repair becomes necessary when the brackets have become worn to a point at which they will no longer securely hold new flights to the inside of the drums. It then becomes necessary to either cut the remaining brackets from the inside of the drums and replace them with new ones, or to rebuild the worn brackets with additional material thicknesses to rejuvinate them for further service.
Another known method of mounting the flights to the inside walls of the drums eliminates the need to replace or repair on a relatively frequent basis such above-described brackets. This is accomplished by providing flight assemblies with mounting ears or flanges extending substantially parallel of the wall of a respective drum. The mounting flanges have apertures which are 4 spaced to line up with correspondingly spaced mounting apertures in the drums. The flights are then mounted by bolts which extend directly through the wall of the respective drum. The bolts are fastened also in a typical manner with nuts. When it comes time to replace the flights, the flanges on the worn flights, extending flat against the apertures in the drums have protected the apertures against wear. The heads of bolts or the respective nuts on the inside of the drums are typically embedded in material accumulations adjacent the drum wall. Consequently, the bolts and nuts are still cut away with a cutting torch to release the worn flights. New flights are then aligned to the existing apertures to attach them to the drum in the same position as the just removed, worn flights.
In replacing the flights of the last-described flight assemblies, a problem exists in that two workers are required to accomplish the initial assembly or a replacement of the worn flights. One worker aligns the flights to the existing apertures in one of the drums and either sticks a bolt through the aperture in the mounting flange of the flight and the aligned aperture in the drum, while a second worker attaches and tightens a nut on the outside of the drum. In the alternative, the bolt is inserted from and held in place on the outside of the drum by one worker, while the second worker attaches the flight and tightens a nut over the inner end of the bolt extending into the drum from the outside.
It is, hence, desirable to devise a mount and a related method of mounting which eliminates some of the cumbersome procedures of assembling or changing flights in a drier-mixer drum.